Spectral Aerosol Radiative Forcing and Efficiency of the La Palma Volcanic Plume over the Izaña Observatory

Abstract

On 19 September 2021, a volcanic eruption began on the island of La Palma (Canary Islands, Spain). The eruption has allowed the assessment of an unprecedented multidisciplinary study on the effects of the volcanic plume. This work presents the estimation of the spectral direct radiative forcing ((Formula presented.) F) and efficiency ((Formula presented.) F (Formula presented.)) from solar radiation measurements at the Izaña Observatory (IZO) located on the island of Tenerife (∼140 km from the volcano). During the eruption, the IZO was affected by different types of aerosols: volcanic, Saharan mineral dust, and a mixture of volcanic and dust aerosols. Three case studies were identified using ground-based (lidar) data, satellite-based (Sentinel-5P Tropospheric Monitoring Instrument, TROPOMI) data, reanalysis data (Modern-Era Retrospective Analysis for Research and Applications, version 2, MERRA-2), and backward trajectories (Flexible Trajectories, FLEXTRA), and subsequently characterised in terms of optical and micro-physical properties using ground-based sun-photometry measurements. Despite the (Formula presented.) F of the volcanic aerosols being greater than that of the dust events (associated with the larger aerosol load present), the (Formula presented.) F (Formula presented.) was found to be lower. The spectral (Formula presented.) F (Formula presented.) values at 440 nm ranged between −1.9 and −2.6 Wm (Formula presented.) nm (Formula presented.) AOD (Formula presented.) for the mineral dust and mixed volcanic and dust particles, and between −1.6 and −3.3 Wm (Formula presented.) nm (Formula presented.) AOD (Formula presented.) for the volcanic aerosols, considering solar zenith angles between 30 (Formula presented.) and 70 (Formula presented.), respectively.